1. Field of the Invention
This invention relates to a toner kit and an image-forming method which are used in image-forming apparatus such as electrophotographic apparatus and printers of an electrophotographic system or electrostatic recording system in which a developer is made to adhere to an electrostatically charged image (latent image) formed on an image-bearing member, rendering the image visible.
2. Related Background Art
Full-color image formation by electrophotography is basically made by combination of a yellow toner, a magenta toner and a cyan toner and optionally a black toner (see, e.g., Japanese Patent Publication No. S53-47176). Then, a full-color copied image is formed by sequentially superimposing three color toners, or four color toners inclusive of a black toner, on a transfer paper, where not only developing performance but also transfer performance are important factors that determine image quality.
In recent years, with wide spread of image-forming apparatus such as full-color copying machines and color laser printers, they also have become used in various purposes, and have come severely required on image quality. For example, in the copying of images such as catalogues and maps, it is demanded to reproduce images very finely and faithfully without crushing or breaking, up to fine details. Also, in image-forming apparatus such as color laser printers making use of digital image signals, latent images are formed by collection of dots with a stated potential, and solid areas, halftone areas and light areas are expressed by change of the area of each dot. In order to achieve high image quality, it is increasingly highly needed to perform not only faithful development of these images but also faithful transfer of developed images.
Electrical resistance of toners can be given as a physical property that has great influence on such transfer. A difference between a high-resistance organic colorant added internally to each color toner and low-resistance carbon black added internally to a black toner causes a difference in their transfer performance. This is a problem always present in full-color image formation. In order to solve the problem on transfer at the time of full-color image formation, a measure is taken by, e.g., making different the amount of fine particles added to a toner base (toner particles) for each station of an image-forming apparatus (e.g., see Japanese Patent Application Laid-Open No. H02-284159), or making the shape of toner particles different by colors (e.g., see Japanese Patent Application Laid-Open No. H11-295931). There is further a proposal that, in an image-forming apparatus having a specific structure, the amount of a fluidity improver added to a black toner base (black toner particles) is made smaller than the amount of a fluidity improver added to each color toner base (color toner particles) to uniform the degree of agglomeration between the black toner and each color toner so that the charging performance can be made stable during running (e.g., see Japanese Patent Application Laid-Open No. 2000-267443.
However, as apparatus are made highly functional, situations are coming in which transfer performance must be much more improved than ever. For example, recently, it is becoming ordinary for the apparatus to be furnished with the function of double-side printing, and it has come demanded to provide an image-forming method which can simply and sufficiently deal with a difference in transfer performance between the first-side printing and the second-side printing in a high-temperature and high-humidity environment that makes designing difficult. Besides, in machines which can print images on a variety of recording mediums but have a secondary transfer mechanism which more tends to cause image deterioration because transfer is performed twice, it has come demanded to faithfully transfer full-color images to transfer materials. Further, there is a high desire to lessen wastes as far as possible. Accordingly, it has come desired to more improve transfer efficiency.